Particle accelerator



Dec. 24, 1968 R. B. HALL ETAL 3,413,206

PARTICLE ACCELERATOR 7 Filed April 8, 1964 2 Sheets-Sheet. 1

W3 L x/z b A INVENTOR. RICHARD B. HALL BY TERENZIO CONSOLI 0 0.5 1 4ATTORNEYS Dec. 24, 1968 R. B. HALL ETAL 3,413,206

PARTICLE ACCELERATOR Filed April 8, 1964 2 Sheets-Sheet z INVENTORSRICHARD B. HALL Y TEREHZIO CONSOLI- fiwymm AT TORN EYS United StatesPatent 3,418,206 PARTICLE ACCELERATOR Richard B. Hall, Bellevue, Wash,and Terenzio (Jonsoli, Paris, France, assignors to The Boeing Company,Seattle, Wash, a corporation of Delaware Filed Apr. 8, 1964, Ser. No.358,179 19 Claims. (Cl. 176--2) ABSTRACT OF THE DISCLOSURE A high energyparticle accelerator is described which makes use of a radio frequencycavity disposed within a longitudinal magnetic field extending betweenopposite openings in the ends of the cavity. The magnetic field isestablished with a field gradient existing within the cavity being ofsuch a magnitude that at one point in the cavity the frequency of the'RF signals applied to the cavity will correspond to the cyclotronfrequency of the particles for the magnetic field at that point. Themagnetic field strength is established to be greater than and less thanthe field strength at said point at respective locations on oppositesides of said point with the arrangement being such that chargedparticles entering the apparatus will be highly accelerated. An improvedevacuation apparatus is disclosed making use of the described particleaccelerator to remove particles from a container. In a furtherembodiment of the invention a pair of the particle accelerators areillustrated in combination with a magnetic bottle for generating hightemperatures.

The present invention relates in general to particle accelerators andmore particularly to an improved accelerator which makes use of magneticfields and electromagnetic radiation to accelerate charged particles ina manner such that the apparatus is adapted for various uses and inparticular for use in propulsion systems, vacuum creating systems, andhigh temperature fusion systems.

It is well know at the present time that charged particles such aselectrons and ions when subjected to an appropriate electric field willbe accelerated and consequently their energy increased. This phenomenonin combination with the etfect of a magnetic field upon chargedparticles has made possible various types of particle ac celerators asfor example the cyclotron, synchroton and accelerators of other types.Such equipment has generally been relatively bulky and heavy andtherefore not particularly well suited for use in propulsion systemswherein the discharge of the accelerated particles can serve to providean opposite thrust to the source of particles. With the growingimportance of the field of study frequently referred to as plasmaphysics a need has also arisen for compact particle accelerators whichcan be used to increase the energy of a plasma composed of chargedparticles.

It is therefore an object of the present invention to provide animproved apparatus for increasing the velocity of electrically chargedparticles and consequently their energy.

It is another object of the present invention to provide an improvedparticle accelerator which can be used as a propulsion system byincreasing the discharge velocity of charged particles at the expense ofmagnetic and electric fields in a manner such that the source of theparticles is accelerated in a direction opposite to the direction ofdischarge of the particles.

It is a further object of the present invention to provide an improvedcompact particle accelerator making use of simplified and ruggedcomponents.

Another object of the present invention is to provide an evacuationapparatus which makes use of an improved particle accelerator tosubstantially completely remove a gas from a container in a manner suchthat a high vacuum is produced within the container.

In accordance with the teachings of the present invention a suitable gasor plasma of charged particles is subjected to a magnetic field andsimultaneously to an alternating electric field which is perpendicularto the axis of the magnetic field and has a field gradient parallel tothe magnetic field. A radio frequency cavity having oppositely disposedopenings is preferably utilized with the magnetic field extendingbetween the tow openings and having a magnetic field gradientestablished therebetween of a particular magnitude such that chargedparticles at a given point intermediate the two openings will have acyclotron frequency corresponding to the frequency of RF signals appliedto the cavity. With the magnetic field gredient between one of theopenings and the point at which the cyclotron frequency of the chargedparticles is equal to the frequency of the applied RF electromagneticenergy being greater than the field strength at said point and with thefield gradient decreasing between said point and the other opening, itis found that charged particles entering the cavity are continuouslyaccelerated within the cavity and hence are discharged at a velocitysubstantially greater than their entrance velocity. The source of theparticles can either be a plasma of charged particles or a natural gaswhich ionizes at the interior of the cavity in the presence of theelectric field'.

By using an enclosed source of a neutral gas as the source of particlesto be accelerated it is found that the enclosed source will beeffectively evacuated as a result of the continued acceleration anddischarge of the gas by the accelerator. Thus an improved evacuationsystem is provided which can be readily used in combination withconventional pumping devices.

In accordance with further teachings of the present invention a pair ofimproved particle accelerators are diametrically opposed so that eachsimultaneously accelerates charged particles into the interior of amagnetic bottle which serves to apply compressional force to the highenergy particles in the interior thereof. Suitable refiecting magneticmirrors are positioned adjacent the two entrances to the magnetic fieldand therefore as a result of the high energy imparted to the particlesby the accelerators and the presence of the compressional magneticforces extremely high temperatures are generated leading to an improvedhigh temperature system useful in fusion experiments.

The above as well as additional advantages and objects of the presentinvention will be more clearly understood from the following descriptionwhen read with reference to the accompanying drawings wherein,

FIGURE 1 is an orthographic projection of one embodiment of the presentinvention which includes a high frequency resonant cavity having asteady magnetic field maintained therein;

FIGURE 2 is a diagram of electric field intensity within the cavity ofFIGURE 1 as established by a suitable RF signal source;

FIGURE 3 is a graph showing one suitable variation in the ratio of thecyclotron frequency to electromagnetic signal frequency with respect tolocation inside the cavity and as established by the apparatus of FIGURE1;

FIGURE 4 is a schematic illustration of a system which includes a pairof improved particle accelerators in combination with a suitablemagnetic bottle for generating high temperatures required in fusionexperiments; and

FIGURE 5 is a schematic illustration showing in cross section animproved evacuation system. utilizing the improved particle accelerator.

Referring now to the drawings and in particular to FIG- URE 1 there isillustrated a cylindrical radio frequency (RF) cavity resonator 1 whichmay be made of copper or other suitable material and advantageouslysilver plated on the interior. The resonator is provided with openings 2and 3 disposed in the opposite ends thereof and each coaxial with thecenter longitudinal axis of the cavity. A source of particles to beaccelerated shown for purpose of illustration as a plasma source 4 iscoupled with the interior of the cavity by the conduit 8 which passesthrough the opening 2. The section 8A of conduit 8 within the cavity ispreferably made of quartz or of suitable glass to allow passage of RFenergy therethrough. The plasma source 4 is adapted to inject a plasmaof charged particles illustrated generally at 4a into the interior ofthe cavity 1 in a direction indicated as being generally parallel to thecentral longitudinal axis thereof. The plasma may include bothpositively and negatively charged particles. If only particles of onepolarity of charge are used then an external neutralizing circuit may beused to prevent a build-up of charge on the apparatus. It should benoted that the particles would actually traverse complex paths in thecavity and therefore the paths indicated in the drawings are only usedas an illustration to show that the particles do have an accelerationcomponent causing them to be accelerated from one end of the cavity tothe other.

A magnetic field is maintained parallel to the central longitudinal axisof the cavity and for purpose of illustration a series of windings 5energized by a suitable DC power source 7 is shown as providing themagnetic field. As described hereinafter, the field established by thehelix or winding 5 exhibits a longitudinal field gradient and thereforefor purpose of illustration the number of windings is shown as beinggreater near one end of the cavity 1A defined by the resonator than nearthe other end thereof. A similar field can be obtained using a pluralityof windings connected in series circuit along and about the cavity withthe separate windings having shunt resistors of different valuesconnected in parallel therewith so that the desired magnetic fieldgradient (described hereinafter) is achieved.

High frequency electromagnetic signals are introduced into the interiorof the resonator 1 from an RF signal source 6 shown schematically asbeing coupled with the interior of the cavity by means of the coaxialcable 6a having the terminating loop 6b secured to the interior of thecavity 1. It should be understood that the manner of coupling of the RFsignal source to the cavity 1A can be accomplished in various ways Wellknown in the art including the use of a conventional waveguide andtherefore a coaxial cable terminated on the interior of the resonator isshown only for the purpose of illustrating that the signals generated bythe source 6 are applied to the interior of the cavity 1. Theelectromagnetic signal energy is applied to the interior of the cavity 1in the TB mode in the example illustrated in FIGURE 1. The resultingelectromagnetic field within the cavity 1 thus has an electric field Ewhich is polarized in the transverse plane of the cavity and exhibits afield gradient along the central longitudinal axis of the cavity 1A.

It is well known that the gradient of a scalar quantity E(x, y, z) is avector with components Eli/8x, 8E/8y, 'aE/az, respectively, on threeorthogonal axes Ox, 0y, Oz.

As discussed with more particularity hereinafter, the gradient of theelectric field E(x, y, z) is defined a VE, Th mean force F, expressed indynes, for the duration of one period of an electromagnetic field actingon a charged particle introduced into the interior of a cavity, as forexample an electron, of a plasma which is confined to or near thevicinity of the longitudinal axis of the cavity and for a uniformmagnetic field is given by the relation:

K 4mw (1b 1 in which b =f /f; e is the charge of the particle, for theelectron equal to 4.8025 l0 electrostatic CGS units,

m the mass of the particle which for an electron is equal to 9.l076 10g, w the radian frequency of the electromagnetic field which is relatedto the frequency f of the latter by the relation w=21rf, f is thecyclotronic frequency of the particle submitted to the action of themagnetic field B, and E represents the amplitude in volts per cm. of theelectric component of the electromagnetic field.

The cyclotron frequency f for the particles of mass m and charge e in amagnetic field B is:

eB mic (2) where c is the velocity of electromagnetic radiation invacuum.

The cavity 1 is preferably of a length corresponding to one-half thewavelength of the electromagnetic signals applied thereto by the source6 and in the example illustrated is resonant in the mode TE FIGURE 2shows the variation of electric field along the axis of the cavity toillustrate the field gradient within the cavity 1 when the length of thecavity corresponds to one-half the wavelength of the applied RF signals.It will be seen in FIG- URE 2 that the field strength correspondsgenerally to a sine wave, starting at zero adjacent to the opening 2,increasing to its maximum in the central transverse plane of the cavity,and then decreasing to zero adjacent the exit opening 3. The sense ofthe variation in amplitude of the electric field along the centrallongitudinal axis determines the sense of the gradient B and thus of thegradient of the square of the amplitude in Equation 1. This gradient isin the left to right direction for the first half of the cavity 1A ofFIGURE 1 between the opening 2 and the transverse symmetry plane, and isin the opposite direction for the second half of the cavitycorresponding to the space between the transverse plane of symmetry andthe exit opening 3. This is indicated by the notations B and E above thecurve of FIGURE 2.

From Equation 1 it will be seen that in the case of a uniform magneticfield such that b is greater than unity throughout the length of thecavity and in the presence of an electric field having a gradient suchas that producing the curve illustrated in FIGURE 2, the mean force Facting on a charged particle such as an electron which enters the cavity1 through the entrance opening 2 would cause the particle to beaccelerated up to the transverse symmetry plane. Since the sense of theelectric field gradient reverses after the particle passes the centralplane of symmetry it will be seen that the particle would be deceleratedbetween the central plane of symmetry and the exit opening 3. Thereforethe particle would leave the cavity through the opening 3 with avelocity approximately equal to the velocity with which the particleentered the cavity. If the ratio of f /f were less than unity throughoutthe length of the cavity, F would be negative for the first half of thecavity so that particles entering opening 2 would be either reflected ordecelerated in the first half of the cavity and accelerated in thesecond half so that again the entrance and exit velocities would beapproximately the same. To maintain the force F of the proper algebraicsense to cause constant acceleration of the particles from the opening 2to the opening 3, it has been ascertained that the amplitude of thefactor b can be varied along the central longitudinal axis of thecavity. The specific variation desired in the ratio of the cyclotronfrequency of the particles to the frequency of the appliedeliectromagnetic field is discussed in greater detail hereina ter.

An analysis of the forces acting upon a charged particle which is closeto the central longitudinal axis of the cavity I and positionedimmediately adjacent the transverse plane of symmetry will beadvantageous at this point. The system 18 designed so that in atransverse plane which for the example shownis the central transverseplane, corresponding to the plane of symmetry, the intensity of themagnetic field in that plane and the frequency of the applied signalsare such that the cyclotron frequency i is equal to the frequency f ofthe electromagnetic field applied to the cavity. The electric fieldintensity as well as the magnetic field intensity are such that each ofthe two quantities varies along the longitudinal or z axis of thecavity. To reflect the effect of such variations in electric field andmagnetic field in the force exerted on a particle in the cavity, thefollowing equations are utilized:

F1=F +F in which:

2 2 e a and F The force F; is the sum of two forces, F due to theelectromagnetic field of radian frequency w; and F due to the motion ofthe particles at the cyclotron frequency in the magnetic field B. Inthese equations z represents the distance of a point on the centrallongitudinal axis from the plane of the opening 2 in the left end of theresonator with the positive direction corresponding to the directionfrom opening 2 toward opening 3. (KB) represents that part of thekinetic energy which is at the cyclotronic frequency.

If the electromagnetic field is intense, the ratio a of the amplitudesof forces P and F,,, can be approximated by the equation:

(Hung? in which k is the wave number equal to 21r/)\ or in the exampleillustrated k=11-/L where L is the length of the resonator.

The value of the cyclotron frequency w which is equal to 21% isproportional to the static magnetic field B, and the variable b=f /f istherefore related to the field B. Consequently, the ratio oc F/l2/F,depends on the variation of the intensity of the static magnetic field Bwith respect to z. In order to give a numerical value to .x and,consequently, to maintain a constant sense for the force F a magneticfield gradient providing a variation in the ratio b with respect tolocation along the central axis (z) defined by an equation b=f(z) ischosen. One such equation is:

in which b represents the value of b measured at the point of entranceof the particles corresponding in the present example to the point atwhich the magnetic field has maximum value. A is the wavelengthexpressed in cm. of the electromagnetic signal which is generally in theorder of one to thirty cm.

The curve in FIGURE 3 is one example of the variation of b with respectto distance from the plane of maximum magnetic field intensity (the leftend of the cavity in the embodiment of FIGURE 1) which produces thedesired result. In FIGURE 3 the value of b is represented on theordinate with the abscissa being in units of ,(z being distance from theopening 2). In the example of FIGURE 3 b, is equal to 1.3. According tothis curve, b is equal to one in the transverse symmetry plane of cavity1A. Consequently, the intensity of the static magnetic field in thisplane is such that the cyclotron frequency of the particles (such aselectrons) is equal to the frequency of the electromagnetic field.Moreover, the slope of the curve shows that there is a gradient of themagnetic field B along the axis of the cavity 1A and such gradientmaintains a constant sense. The intensity of the magnetic field will beseen to be of a first intensity in a first region adjacent opening 2 andto the left of the plane of symmetry; of a second intensity less thansaid first intensity in a second region corresponding to the plane ofsymmetry in which the intensity establishes the cyclotronic frequency fand of a still lower third intensity in the third region adjacent saidexit opening 3.

The gradient of the static magnetic field illustrated in FIGURE 3 servesto maintain the direction of the force F constant and thereforeparticles entering the cavity through the opening 2 are constantlysubjected to an appropriate accelerating force. Each particle of mass min the equations previously set forth (as for example the mass of anelectron) is therefore subjected to the force F As a result of theconstant acceleration of the charged particles of mass m it will be seenthat a space charge of such particles will exist between the openings 2and 3. In the case where the particles of mass m are electrons, any ionsin the plasma will be accelerated through the cavity as a result of andunder the influence of the space charge caused by the preferentialacceleration of the electrons by the field. It will be seen fromEquation 1 that the accelerating force which acts on particles in thefield is inversely proportional to the mass of the particles andtherefore electrons are more rapidly accelerated than are ions. The ionshowever are entrained and accelerated by the space charge associatedwith the electrons and hence will be subjected to a force which is inthe same sense as is the force F The intensity of the static magneticfield in the central plane can be adjusted to provide therein acyclotron frequency of i for the ions together with a correspondinglower frequency electromagnetic field so that the ions can be directlyaccelerated.

From the above it will be seen that by providing a mag netic fieldhaving a first intensity in a transverse plane of the cavitycorresponding to a field strength such that the cyclotron frequency ofparticles in that plane is equal to the frequency of the appliedelectromagnetic field and with the gradient of the magnetic field beingsuch that the field strength on opposite sides of said plane isrespectively greater and less than said first intensity, particles arecontinuously accelerated throughout the length of the cavity. As setforth above, the source of particles 4 can be any of a number well knownin the art and adapted to apply a plasma to the cavity 1A. A neutral gaswhich ionizes at the interior of the cavity 1 in the presence of theintense electric field therein can also serve as the source ofparticles. In each case particles are ejected from the opening 3 with avelocity which is greater than the entrance velocity thereof. As aresult of the increased velocity of the particles it will be seen thatan oppositely directed reaction force will be applied to the walls ofthe cavity and hence a propulsion system is provided.-It has been foundthat when the strength of the applied electromagnetic energy is in theorder of 200 kilowatts a thrust in the order of .02 Newton is obtained.

Referring now to FIGURE 4 there is illustrated a system which includestwo improved particle accelerators in combination with a suitablemagnetic bottle to provide a high temperature fusion apparatus. Thefirst plasma or particle accelerator will be seen to include a cavityresonator 11 having inlet and outlet openings 12 and 13 positioned inopposite ends thereof and located coaxially with respect to the centrallongitudinal axis of the cavity. A first plasma or particle source 14 isadapted to supply a first plasma 14a to the interior of the resonantcavity 11A by being connected with the entrance opening 12. The windingshown generally at 15 provides the required coaxial magnetic field alongthe central longitudinal axis of the cavity 11. A radio frequency supply16 is coupled to the interior of the cavity 11 by the waveguideillustrated generally at 16A. For purpose of illustration a source of DCpotential illustrated as a battery 17 will be seen to be connectedthrough a variable impedance element to the winding 15.

The exit opening 13 of the first plasma accelerator will be seen to bedirectly communicating with the interior of a chamber 18A provided bythe enclosure member 18 which is shown for purpose of illustration ashaving an elliptical cross section. The member 18 preferablycommunicates directly with the plasma source 14 with the section 18Bthereof which is inside cavity 11A preferably being made of quartz orother suitable material which permits the passage of RF energytherethrough and also to permit evacuation of the system. The fluxrequired for applying magnetic pressure to the particles introduced intothe chamber 18A can be'provided by.a number of systems well known at thepresent time. For example pairs of straight conductors forming the sidesof a right circular cylinder and referred to as a cusped arrangementhaving current passed in opposite directions through adjacent conductorswill provide the required confining magnetic field. For purpose ofillustration in FIGURE 4 an elongated generallycylindrical winding 19which is suitably energized by a power supply (not shown) provides therequisite field commonly referred to in the art as a magnetic bottle orcylinder.

At the right end of the chamber 18 it will be seen that a second plasmaaccelerating apparatus substantially identical to the apparatus shown atthe left end thereof is provided. This second accelerator includes: asecond resonator 21 defining a cavity 21A having entrance and exitopenings 22 and 23; a second plasma source 24 providing the plasma 24A;a second electromagnet 25; RF supply 26 coupled to the interior ofcavity 21 by the waveguide 26A; and a second DC power supply 27. Thecavities 11A and 21A are each one half wavelength long and resonant atthe frequency of the RF sources 16 and 26 with the electromagnets andproviding the fields previously described. The section 18C of the member18 within cavity 21A is preferably quartz. The two particle acceleratingsystems will thus be seen to be oppositely directed for simultaneouslyapplying accelerated particles to the interior of chamber 18A. As iswell known in the art, the winding 19 serves to apply magnetic pressureto the moving charged particles but also the ends thereof act asmagnetic mirrors to prevent the escape of charged particles from thechamber 18A. Further details of the apparatus for applying pressure tothe charged particles introduced in the cavity 18A are not includedherewith since any of a number of the various types of apparatus wellknown in the art are suitable for use in the system of FIGURE 4. It isof importance to note, however, that the ultimate temperature achievedin the fusion apparatus is increased as the entrance energy (orvelocity) of the plasma particles is increased and therefore through theuse of the two plasma accelerators a very high temperature can beachieved. Thus a simplified and effective high temperature apparatus isprovided which is well suited for laboratory use. It is of courseobvious that a single accelerator together with an appropriate magneticpressure system can be provided.

Since the simplified particle accelerating apparatus of FIGURE 1 servesto continuously receive low energy particles and discharge the same atan increased velocity it has been found that the apparatus is suitablefor use for evacuating an enclosed chamber such as for example a chamberhaving a gas therein. Thus in the embodiment of the inventionillustrated in FIGURE 5 it will be seen that a container 39 defines anenclosed chamber 39A which is substantially spherical in shape and iscoupled with the entrance opening 32 of a resonator 31 defining a cavity31A. The exit opening 33 of the cavity is coupled by means of theenclosed conduit 39 with the intake port of a conventional evacuationpump 40 having a discharge opening 41. A magnetic field is providedparallel to the central longitudinal axis of the resonator 31 by theelectromagnet 35 shown for purpose of illustration as being energized bya suitable battery 37. The magnetic field provided parallel to thecentral longitudinal axis of the resonator 31 exhibits the fieldgradient requirements set forth in connection with the embodiment of theinvention illustrated in FIGURE 1. It will also be seen in FIGURE 5 thata source of RF energy 36 is coupled by means of the coaxial cable 36Awhich terminates at 36B in the interior of the RF cavity 31 so that anRF field will be established in the interior of the cavity 31. Thelength of the resonator 31 is preferably chosen to be equal to one halfthe Wavelength of the RF signals applied to the interior thereof by thesupply 36. The intensity of the magnetic field in the central transverseplane of the cavity 31 as established by the electromagnet 3,5,is suchthat the cyclotron frequency of the ionized gas particles in that planeis equal to the frequency of the signals provided by the radio frequencysupply 36. As a result of the magnetic field gradient from left to rightdown the central longitudinal axis of the resonator 31 and theelectromagnetic field inside the cavity 31A neutral gas particlesentering the cavity opening 32 will be ionized and then continuouslyaccelerated from left to right down the resonator 31. The pump 40 servesto initially create a low pressure to start the movement of the gas fromthe chamber 39A into the interior of the cavity 31A and then serves tocontinuously remove the particles discharged through opening 33. As aresult of the operation of the apparatus in FIGURE 5 an extremely highvacuum is created within the chamber 39.

There has thus been disclosed an improved compact particle acceleratorand systems having various uses including those of a propulsion system,an evacuation device, and as an apparatus for use in combination with amagnetic confinement system to provide a high temperature apparatus.Those modifications and changes which will be obvious to a personskilled in the art from the above description and accompanying drawingsof illustrative embodiments are intended to be encompassed by thefollowing claims.

What is claimed is:

1. A particle accelerating apparatus comprising in combination: meansdefining a radio frequency cavity having a particle entrance opening anda particle exit opening; signal input means adapted to applyelectromagnetic signals of frequency f to said cavity to establish anelectric field gradient E between said openings wherein the gradient ispositive in a first section and negative in a second section; andmagnetic field means establishing a magnetic field in said cavity havingan intensity gradient between said openings which maintains the ratio f/f greater than 1 Where V E is positive and less than one where B isnegative with f being the cyclotron frequency established by saidmagnetic field for particles of mass m and charge e which are to beaccelerated.

2. A particle accelerating apparatus in accordance with claim 1 whereinsaid cavity is of a length equal to an integral multiple of one half thewavelength of signals at said frequency f and wherein said magneticfield means provides a magnetic field of an intensity such that saidratio f /f is equal to one at a point between said openings in saidcavity.

3. A particle accelerator comprising in combination: means defining aradio frequency cavity resonant at a frequency f and having first andsecond opposed openings therein adapted to permit particles to passtherethrough; means establishing a magnetic field in said cavityextending in a direction from said first to said second opening andhaving an intensity gradient between said openings and with theintensity of said field in a first region in said cavity establishing acyclotron frequency of f which is equal to said frequency f forparticles of mass m and charge e; and means for applying electromagneticsignals of said frequency f to said cavity, the length of the cavity andsaid frequency being such that an electric field is establishedperpendicular to said direction and having a positive gradient in afirst region of said cavity and a negative gradient in a second regionof said cavity.

4. A particle accelerator in accordance with claim 3 wherein the lengthof said cavity is equal to one half the Wavelength of said signals atsaid frequency f.

5. A particle accelerator in accordance with claim 3 wherein theintensity of said magnetic field in a second region between said firstopening and said first region is greater than the intensity in saidfirst region and the intensity of said magnetic field in a third regionbetween said first region and said second opening is less than theintensity in said first region.

6. A particle accelerator in accordance with claim- 5 wherein the lengthof said cavity is equal to one half the Wavelength of signals at saidfrequency f.

7. A particle accelerating system comprising in combination: meansdefining a radio frequency cavity having first and second openingstherein; means establishing a magnetic field extending in a firstdirection from said first opening to said second opening and having agradient such that the intensity of said magnetic field is greater insaid first opening than in said second opening and the intensity at apoint intermediate said two openings establishes a cyclotron frequency ifor particles of mass m and charge e; means for applying electromagneticsignals at said frequency f to said cavity, the length of the cavity andsaid frequency 1 being such that an electric field is establishedperpendicular to said first direction and having a positive gradient ina first portion of the cavity and a negative gradient in a secondportion of the cavity; and means for injecting particles of said mass mand charge e through said first opening into said cavity.

8. A particle accelerator in accordance with claim 7 wherein said cavityis of a length equal to one half the wavelength of said signals atfrequency f and wherein said signals are applied to said cavity in a TEmode.

9. A particle accelerator in accordance with claim 7 wherein said lastnamed means includes a plasma source, and conduit means coupling saidsource with said cavity and extending between said first and secondopenings.

10. A particle accelerator comprising in combination: a cavity resonatorhaving a first opening for receiving particles to be accelerated and asecond opening for discharging particles; means establishing a magneticfield in said resonator with the direction thereof extending betweensaid openings, said magnetic field being of a first intensity in a firstregion within said resonator adjacent said first opening, of a secondintensity less than said first intensity in a second region within saidresonator, and of a third intensity less than said second intesity in athird region adjacent said second opening; and means establishingelectromagnetic signals within said resonator with the electric fieldcomponent thereof being transverse to a line extending between saidopenings and having a positive electric field gradient between saidfirst and second regions and a negative field gradient between saidsecond and third regions.

11. A particle accelerator in accordance with claim 10 wherein saidsecond intensity is equal to B Where B is proportional to fmc/ e, wheref=the frequency of said signals, m=the mass of a particle to beaccelerated, c=the velocity of an electromagnetic wave in vacuum, ande=the electric charge of a particle to be accelerated.

12. A particle accelerator in accordance with claim 10 wherein saidcavity resonator is resonant at a frequency f and wherein the length ofsaid cavity resonator is equal to one half the wavelength ofelectromagnetic signals at said frequency f.

13. A particle accelerator in accordance with claim 11 wherein saidcavity resonator is of a length equal to one half the wavelength ofelectromagnetic signals at said frequency f.

14. A particle accelerator in accordance with claim. 10 wherein saidmagnetic field has a constant gradient between said openings.

15. A particle accelerator in accordance with claim 10 and includingparticle conduit means extending between said openings in said cavitycomposed of a material adapted to permit the passage of radio frequencyenergy through the walls thereof.

16. An evacuation system comprising in combination: means defining aradio frequency cavity having first and second openings at opposite endsthereof; means for applying electromagnetic signals to said cavity at afrequency f, the length of the cavity and said frequency f being suchthat an electric field is established perpendicular to a directionextending from said first to said second opening with the field having apositive gradient in a first portion of the cavity and a negativegradient in a second portion of the cavity; means establishing amagnetic field between said openings in said cavity with the intensityof said field decreasing with increasing distance from said firstopening and of a magnitude at a point intermediate said two openingssuch that a cyclotron frequency equal to said f is established forparticles of mass m and charge 2; means defining a chamber to beevacuated having an opening therein coupled with said first opening ofsaid cavity; and pressure reduction means coupled with said secondopening of said cavity.

17. A system in accordance with claim 16 wherein said cavity is of alength corresponding to one half the wavelength of a signal at saidfrequency f.

18. An apparatus for accelerating and confining charged particlescomprising in combination: means defining a first radio frequency cavityhaving first and second aligned openings therein; a source of particlesto be accelerated; means defining an enclosed chamber; conduit meansextending from said source through said first and second openings andcoupled with said chamber to permit passage of particles from saidsource through said cavity to said chamber; first magnetic field meansdisposed about said chamber adapted to provide a confining magneticfield therein; second magnetic field means adapted to provide a magneticfield extending between said openings having a first intensity at apoint intermediate said openings to establish a cyclotron frequency of ffor particles of mass m and charge 2 and further.being of a secondintensity greater than said first intensity adjacent said first openingand of a third intensity less than said first intensity adjacent saidsecond opening; and means applying electromagnetic signals at saidfrequency f to said cavity, the length of the cavity and said frequencybeing such that an electric field is established perpendicular to adirection extending from said first to said second opening with thefield having a positive gradient in a first portion of the cavity and anegative gradient in a second portion of the cavity.

19. An apparatus in accordance with claim 17 wherein the length of saidcavity is equal to one half the wavelength of signals at said frequency1.

References Cited UNITED STATES PATENTS 2,817,045 12/1957 Goldstein etal. 315-39 3,151,259 12/1964 Gloersen et al. 313-63 3,179,838 4/1965Adler 315-3 3,221,212 11/1965 Gorowitz et al. 313-231 X 3,257,579 6/1966Delcroix et a1. 313-63 X HERMAN KARL SAALBACH, Primary Examin r. S.CHATMON, In, Assistant Examiner.

U.S. Cl. X.R. 176-5; 315-111, 39; 103-1; 313-63; 310-11

